The present invention relates to an improved process for deasphalting resid and substantially removing cracking catalyst fines from decanted oil.
Catalytic cracking of oil is an important refinery process which is used to produce gasoline and other hydrocarbons. During catalytic cracking, the feedstock, which is generally a cut or fraction of crude oil, is cracked in a reactor under catalytic cracking temperatures and pressures in the presence of a catalyst to produce more valuable, lower molecular weight hydrocarbons. Gas oil is usually used as a feedstock in catalytic cracking. Gas oil feedstocks typically have a boiling range from 650.degree. F. to 1000.degree. F. and less than 1% RAMS carbon by weight. Gas oil feedstocks also typically contain less than 5% by volume naphtha and lighter hydrocarbons having a boiling temperature below 430.degree. F., from 10% to 30% by volume diesel and kerosene having a boiling range from 430.degree. F. to 650.degree. F., and less than 10% by volume resid having a boiling temperature above 1000.degree. F. It is desirable to provide an effective process to increase the yield of gasoline (naphtha) in catalytic cracking units.
It has been known to deasphalt and catalytically crack virgin unhydrotreated, low sulfur resid as well as to deasphalt, subsequently hydrotreat, and catalytically crack high sulfur resid. However, better demetalization and higher resid conversion are desirable.
Furthermore, such prior art processes produce hydrogen-rich asphaltenes which are difficult and expensive to handle and process, melt (liquify) at relatively low temperatures, and which cannot be used as solid fuel. Asphaltenes are difficult to blend into fuel oils, and are not generally usable and desirable for asphalt paving or for use in other products.
In the past, spiraling oil costs and extensive price fluctuations have created instability and uncertainty for net oil consuming countries, such as the United States. It has been difficult to attain adequate supplies of high-quality, low-sulfur, petroleum crude oil (sweet crude) from Nigeria, Norway, and other countries at reasonable prices for conversion into gasoline, fuel oil, and petrochemical feedstocks. In an effort to stabilize the supply and availability of crude oil at reasonable prices, Amoco Oil Company has developed, constructed, and commercialized extensive, multimillion dollar refinery projects under the Second Crude Replacement Program (CRP II) to process poorer quality, high-sulfur, petroleum crude oil (sour crude) and demetalate, desulfurize, and hydrocrack resid to produce high-value products, such as gasoline, distillates, catalytic cracker feed, metallurgical coke, and petrochemical feed-stocks. The Crude Replacement Program is of great benefit to the oil-consuming nations since it provides for the availability of adequate supplies of gasoline and other petroleum products at reasonable prices while protecting the downstream operations of refining companies.
During resid hydrotreating, such as under Amoco Oil Company's Crude Replacement Program, resid oil is upgraded with hydrogen and a hydrotreating catalyst to produce more valuable lower-boiling liquid products. However, undesirable carbonaceous solids are formed during resid hydrotreating. These solids have been characterized as multicondensed aromatics which form and precipitate from cracking of the side chains of asphaltenes. These carbonaceous solids are substantially insoluble in hexane, pentane, and in the effluent hydrotreated product oil. The solids become entrained and are carried away with the product. Such solids tend to stick together, adhere to the sides of vessels, grow bigger, and agglomerate. Such solids are more polar and less soluble in other hydrocarbons than the residual oil feedstock. Carbonaceous solids are produced as a reaction by-product during ebullated bed hydrotreating (expanded bed hydrotreating). During ebullated bed hydrotreating, the ebullating hydrotreating catalyst fines can serve as a nucleus and center for asphaltene growth. The situation becomes even more aggravated when two or more hydrotreating reactors are connected in series as in many commercial operations. In such cases, solids formed in the first reactor not only form nucleation sites for solids growth and agglomeration in the first reactor, but are carried over with the hydrotreated product oil into the second reactor, etc., for even larger solids growth and agglomeration.
The concentration of carbonaceous solids increases at more severe hydrotreating conditions, at higher temperatures and at higher resid conversion levels. The amount of carbonaceous solids is dependent on the type of feed. Operability at high resid conversion is limited by the formation of carbonaceous solids.
Solids formed during resid hydrotreating cause deposition and poor flow patterns in the reactors, as well as fouling, plugging, and blocking of conduits and downstream equipment. Oils laden with solids cannot be efficiently or readily pipelined. Hydrotreating solids can foul valves and other equipment, and can build up insulative layers on heat exchange surfaces reducing their efficiency. Buildup of hydrotreated solids can lead to equipment repair, shutdown, extended downtime, reduced process yield, decreased efficiency, and undesired coke formation.
Decanted oil (DCO) is a valuable solvent and is used advantageously in the resid hydrotreating unit for controlling the carbonaceous solids therein. However, decanted oil is normally obtained from a catalytic cracking unit and contains cracking catalyst solids or fines therein. These fines are small particles made up of the catalyst used in the catalytic cracking unit.
For a fluid catalytic cracking unit, the preferred cracking catalysts are those containing crystalline aluminosilicates, zeolites, or molecular sieves in an amount sufficient to materially increase the cracking activity of the catalyst, e.g., between about 1 and about 25% by weight. The crystalline aluminosilicates can have silica-to-alumina mole ratios of at least about 2:1, such as from about 2 to 12:1, preferably about 4 to 6:1 for best results. The crystalline aluminosilicates are usually available or made in sodium form. This component is preferably reduced, for instance, to less than about 4 or even less than about 1% by weight through exchange with hydrogen ions, hydrogen-precursors such as ammonium ions, or polyvalent metal ions.
Suitable polyvalent metals include calcium, strontium, barium, and the rare earth metals such as cerium, lanthanum, neodymium, and/or naturally-occurring mixtures of the rare earth metals. Such crystalline materials are able to maintain their pore structure under the high temperature conditions of catalyst manufacture, hydrocarbon processing, and catalyst regeneration. The crystalline aluminosilicates often have a uniform pore structure of exceedingly small size with the cross-sectional diameter of the pores being in a size range of about 6 to 20 angstroms, preferably about 10 to 15 angstroms.
Silica-alumina based cracking catalysts having a significant proportion of silica, e.g., about 40 to 90 weight percent silica and about 10 to 60 weight percent alumina, are suitable for admixture with the crystalline aluminosilicate or for use as such as the cracking catalyst.
The decanted oil cracking catalyst fines are more abrasive than resid hydrotreating unit (RHU) fines. The cracking catalyst fines in decanted oil are abrasive and have a tendency to put undue wear on the valves and various feed product controls used to convey the decanted oil during its use as a solvent.
Our U.S. Pat. No. 4,940,529 teaches a solvent extraction deasphalting unit for hydrotreated resid from vacuum tower bottoms. The solvent extraction unit comprises a mixer and two or three separator vessels or zones operated slightly below or above the supercritical conditions of the solvent.
Our U.S. Pat. No. 4,808,298 is directed to resid hydrotreating and to a minimization of the formation of carbonaceous solids from hydrotreating. Pat. No. 4,808,298 does this by treating the resid oil feedstock or hydrotreated oil with an aromatic diluent such as decanted oil obtained from the decanted oil line of a fluid catalytic cracker unit. The process illustrated in U.S. Pat. No. 4,808,298 injects the decanted oil diluent into the atmospheric tower and the vacuum tower.
Over the years a variety of processes and equipment have been suggested for refining operations. Typifying some of those prior art processes and equipment are those described in U.S. Pat. Nos:
______________________________________ 2,360,272 3,579,436 4,302,323 4,486,295 2,382,382 3,635,815 4,305,814 4,495,060 2,398,739 3,661,800 4,331,533 4,502,944 2,398,759 3,681,231 4,332,674 4,521,295 2,414,002 3,766,055 4,341,623 4,040,958 2,425,849 3,796,653 4,341,660 4,525,267 2,436,927 3,838,036 4,381,987 4,526,676 2,755,229 3,844,973 4,391,700 4,592,827 2,879,224 3,905,892 4,400,264 4,606,809 2,884,303 3,909,392 4,405,441 4,617,175 2,981,676 3,923,636 4,434,045 4,618,412 2,985,584 3,948,756 4,439,309 4,622,210 3,004,926 4,082,648 4,446,002 4,640,762 3,039,953 4,137,149 4,447,313 4,655,903 3,168,459 4,158,622 4,451,354 4,661,265 3,338,818 4,176,048 4,454,023 4,662,669 3,351,548 4,191,636 4,457,830 4,673,485 3,513,087 4,239,616 4,457,831 4,681,674 3,563,911 4,285,804 4,478,705 4,686,028 3,364,136 4,290,880 4,485,004 4,692,318 4,695,370 4,743,356 4,767,521 4,773,986 4,720,337 4,753,721 4,769,127 4,808,289 4,818,371 ______________________________________
It is, therefore, desirable to provide an improved process for substantially reducing the amount of cracking catalyst fines in decanted oil and to provide an improved process for deasphalting resid.